The invention relates to vehicle suspension systems for dual axle vehicles in which the axles are attached to equaliser beams or more commonly known as walking beams, so that the vehicle load is transferred to the road surface either equally, or in proportion, to the position of the beam pivot to the beam centre.
Various vehicle suspensions have been developed for dual axle vehicles in which the axles are attached to walking beams with a springing medium located between the beam pivot and the vehicle chassis to absorb shocks caused by uneven road conditions. Additionally a mechanical connection system is used between the walking beam and the chassis to firstly transmit tractive effort and torque; secondly to absorb braking effort and torque; and thirdly to constrain the lateral relationship of the axles with the chassis. In the case where the springing mechanism uses steel springs, the spring is usually a multi-leaf semi elliptical type or a taper leaf type, having an eye at the forward end and a slipper surface at the rear end. The spring and its associated saddle then performs all or part all of the required functions of the mechanical connection system. In the case where the springing mechanism uses rubber springs, or air springs, the mechanical connection systems are usually vertical drive pins and load cushions located in vertical aligned rubber bushings.
Air suspensions are generally recognised as having desirable features including superior ride comfort for the driver; enhanced impact protection for the vehicle and cargo; and reduced road impact and consequent road wear. Air suspension with walking beams and vertical drive pins have the benefits of previously mentioned desirable features reduced because the vertical drive pins and associated bushings tend to restrict vertical freedom of the suspension.